Field of the Invention
The invention pertains to the field of butterfly valve seals. More particularly, the invention pertains to mechanically retained butterfly valve seals.
Description of Related Art
Butterfly valves generally include a hollow valve body with an inlet and an outlet, and cylindrical flow channel passing between the inlet and the outlet. A vane is rotatably mounted between the inlet and the outlet on an operating stem passing laterally through the hollow valve body. When the operating stem is rotated, the vane may be rotated between a first position perpendicular to a flow direction between the inlet and the outlet, and a second position parallel to the flow direction. An annular elastomeric seal mounted circumferentially in the cylindrical flow channel at the location of the vane mates with a seat ring on the vane when the vane is in the first position, creating a fluid tight seal between the vane and the cylindrical flow channel of the hollow valve body.
In the prior art, various constructions have been used to mount the elastomeric seal in the cylindrical flow channel. In some constructions, the elastomeric seal is bonded to a channel formed in a surface of the cylindrical flow channel using adhesives. Such constructions, however, do not facilitate field replacement of the elastomeric seal, and also may not provide for adjustment of the elastomeric seal. Additionally, experience has shown that bonded elastomeric seal interfaces may fail under high flow velocity conditions.
In other prior art constructions, the elastomeric seal is compressed into a seal channel and against a seal flange by a retaining ring connected to the seal flange using a number of bolts or screws. This arrangement allows for field replacement of the elastomeric seal, and also for adjustment of the elastomeric seal by changing the torque on the screws or bolts holding the retaining ring, and thus the compression of the elastomeric seal between the retaining ring and the seal flange. This type of construction increases machining required during construction of the hollow valve body, and therefore also manufacturing costs.
An elastomeric seal arrangement described by Kennedy (U.S. Pat. No. 4,763,877, issued 1988) also uses an elastomeric seal compressed into a seal channel and against a seal flange by a retaining ring. In this construction, the retaining ring is held in place by at least three J-shaped clips. The elastomeric seal is first placed in the seal channel. The retaining ring is then located next to the elastomeric seal, and pressure is applied to the retaining ring to compress the elastomeric seal, and move the retaining ring past a channel formed in the surface of cylindrical flow channel.
A long end of the J-shaped clips is received by the groove in the surface of the cylindrical flow channel, and a short end of the J-shaped clips is received by a first groove in the retaining ring. When pressure is removed from the retaining ring, the elastomeric seal decompresses and forces the retaining ring against the J-shaped clips. The long end of the J-shaped clips is in turn forced against a side of the groove in the surface of the cylindrical flow channel, holding the J-shaped clips in place. A point-punch may be used to create a deformation of the J-shaped clips into a second groove formed in the retaining ring, so that the J-shaped clips may only be removed using considerable force. The elastomeric seal may be adjusted by inserting a shim between the long end of the J-shaped clips and the side of the channel in the surface of the cylindrical flow channel, thus increasing the compression of the elastomeric seal into the seal channel and against seal flange.
The annular elastomeric seals used in the prior art are generally formed using extrusion or molding techniques to produce an annular seal with a given cross-sectional profile. However, this method of construction limits the types of elastomers that may be used to form the elastomeric seals because not all elastomeric materials lend themselves to these manufacturing techniques. As a result, butterfly valves used to regulate flow in fluid systems carrying aggressive chemicals may require short service intervals between elastomeric seal replacements. For example, in clean water treatment facilities that use concentrated sterilization fluids to clean piping systems, improper flushing of the sterilization fluids after a cleaning cycle may lead to rapid elastomeric seal degeneration, and failure of elastomeric seals.